This proposal seeks to elucidate the mechanisms which lead to the development of cholesteatoma and associated bone resorption in chronic otitis media. Cholesteatoma will be induced by injection of a propylene glycol solution into the middle ear cavity of rats. The resulting epidermal structures and associated bone resportion will be measured by morphometric analysis using computerized image analysis measuring total volume of bone resorption form serial sections. The expression of intracellular keratin products in epidermal keratino-cytes associated with development of cholesteatoma will be studied in experimental animals. This will be accomplished immunohistochemically with four different types of monoclonal anti-keratin antibodies. Each specimen will be assessed to make two determinations: 1) present or absent, and 2) predominate type of keratins. Langerhans cells which are antigen presenting cells and found in cholesteatoma will be determined immunohistochemically using monoclonal anti- T- 6 antigen. Immunohistochemical studies of keratin subclasses and Langerhans cells will be also performed on human tissues to compare with and assess validity of our animal model. The enhancing rate of cholesteatoma development and bone resorption that occurs as a consequence of infection will be studied using bacteria endotoxin and lipoteichoic acid to mimic infection in the experimental animals. Retinoic acid and its analogues, indomethacin, ibuprofen, calcitonin, and vitamin D3 will be given to animals orally, to determine if these agents will inhibit the development of cholesteatoma and/or bone resorption. Cell to cell interactions evoking keratinocyte proliferation and differentiation, particularly interactions with Langerhans cells and T-lymphocytes will be studied to determine factors transmitted between cell types. These in vitro studies combined with in vivo studies will help elucidate the mechanisms leading to the development of cholesteatoma and associated bone resorption.